This exploratory study is designed to ensure the safety of HIV-infected volunteers who complete research protocols that include an analytic treatment interruption (ATI). This is a prospective cohort study of volunteers who were diagnosed with HIV during early acute HIV infection, treated with antiretroviral therapy (ART) and subsequently enrolled in a clinical study that included ATI. After completion of study participation that involves ATI, participants will be recruited into this study for continued clinical and laboratory monitoring. Participants without any indication for resumption of ART and who desire to remain off ART at the time of entry into this study will be monitored closely for HIV viremia and other pre-defined criteria for ART resumption. Participants with any indication for ART at the time of enrollment into this protocol, including patient preference for resumption of ART, will be monitored closely for virologic and immunologic response to ART.